Surfaces of a fluid machine, a pipe, or other structures in a fluid are damaged by various phenomena such as cavitation erosion or corrosion, or solid particle impact. This prevents desired fluid performance from being maintained or reduces strength of the structures. For such phenomena, establishing a technique of predicting development of damage is a major challenge. This application particularly notes prediction of cavitation erosion.
Cavitation erosion is a phenomenon such that cavitation occurs in a low pressure portion in a flow path of a fluid machine or the like, and when this disappears in the downstream, impulsive pressure is generated to erode a surface of the fluid machine or the like. Since the development of the cavitation erosion reduces strength of a structure such as a fluid machine or efficiency of the fluid machine as described above, prediction of the cavitation erosion is extremely significant. For the cavitation erosion, prediction of risk of surface erosion in a stage without any deformation based on CFD (computational fluid dynamics), and construction of a theoretical model of damage in a relatively minute scale of a material surface have been partly proposed. FIG. 10 shows a photograph of a pump casing with actually developing erosion, FIG. 10(A) shows the entire pump casing, and FIG. 10(B) shows a portion with significantly developing erosion shown by the arrow in FIG. 10(A).
As a related technique disclosing a method for predicting an amount of erosion due to cavitation, a technique using soft metal is proposed (see Patent Document 1).
The prediction method includes:
1) predicting a generation position of cavitation erosion in a model fluid machine or an actual fluid machine,
2) forming the generation position by using a soft metal,
3) operating the fluid machine to cause erosion on a surface of the soft metal,
4) measuring an amount of deformation due to the erosion using measurement means,
5) calculating, based on the deformation amount, a deformation speed that is a time change of the deformation amount,
6) calculating cavitation intensity using a database on a relationship between the deformation speed and the cavitation intensity, and
7) predicting the amount of erosion due to cavitation based on the cavitation intensity.
Also, using vibration or noise as an index of an erosion amount or an erosion risk has been also proposed. (see Patent Document 2).
Patent Document 1: JP-A-2007-327455
Patent Document 2: JP-A-H11-37979